Graduate Thesis Or Dissertation
 

A biological and systematic study of the armored boreid, Caurinus dectes, with comparative notes on related mecoptera

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  • Caurinus dectes Russell is a minute, brachypterous scorpionfly which was discovered at Marys Peak, Benton County, Oregon, in 1976, and subsequently described as the only representative of the subfamily Caurininae within the Boreidae (snow scorpionflies). Caurinus dectes is now known to range from the Olympic Peninsula and Northern Cascades in Washington, to northern Lane County, Oregon. The habitats of C. dectes include moist, forested sites with both coniferous and deciduous canopies. Larvae and adults have been found in bryophytes occurring as epiphytes, or on logs and stumps, and in terrestrial stands of mosses and liverworts. Feeding studies showed that both adults and larvae of Caurinus are specialized feeders on leafy liverworts (Jungermanniales). Twenty-five species of Jungermanniales in 15 genera were highly acceptable to adults, while 11 species in 10 genera were accepted slightly, if at all. Adults of C. dectes fed to some degree on two of four genera of the thalloid Metzgeriales, while liverworts of the Marchantiales and Anthocerotae were not accepted at all. Larval feeding preferences paralleled those of adults. The eggs of C. dectes are glued to the leaves of the host liverworts. Eggs hatch in spring, but some eggs may remain in diapause for a year or more. Larval feeding is within the shoot tissues, and is completed within 2 to 3 months of eclosion. There appear to be 3 larval instars. The fully grown larva constructs a silk-lined pupal cell within or under the substrate. The pupal molt occurs between July 1 and August 15, adult emergence is between September 1 and October 15. The major period of adult activity extends from eclosion to April. Mating and oviposition may occur through most of this period. There is evidence that some fraction of the adult population may perenniate. The univoltine life cycle, probable perenniation of adults, and extended egg diapause all are unusual within the Boreidae. The external morphology of larva and pupa, and internal and external morphology of adults are described. The larva is curculioniform, as compared with the scarabaeiform larvae of other Boreidae; the pupa is decticous and exarate. The most aberrant structures of adult Caurinus (cf. other Boreidae), the short rostrum and retractable postabdomen of the female, are probably adapted to the dorsoventral organization of the host liverworts. C. dectes is highly specialized, but a number of characters are primitive with respect to other boreids. These characters justify the recognition of Caurinus as the sister- group of all other boreids. Certain characters of C. dectes, including the free cerci of the female, support the view that the Boreidae are not closely related to other mecopteran families.
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